Downhole tools are used for operations inside boreholes of oil and gas wells. Downhole tools operate in a very harsh environment and must be able to withstand inter alia corrosive fluids, very high temperatures and pressure.
To avoid unnecessary and expensive disturbances in the production of oil and gas, the tools deployed downhole have to be reliable and easy to remove from the well in case of a breakdown. Tools are often deployed at great depths several kilometers down the well, and removing jammed tools are therefore a costly and time-consuming operation.
Well tools are often part of a larger tool string containing tools with different functionalities. A tool string may comprise both transportation tools for transporting the tool string in the well and operational tools for performing various operations downhole.
Various principles for downhole transportation tools, also denoted well tractors, have been developed and tested. The transportation tools are primarily used for transporting tool strings in horizontal or close to horizontal parts of the well where gravity is insufficient for driving the tool string forward.
Downhole tools are complex mechanical constructions, often with multiple functionalities, yet they have to be reliable and capable of functioning in a harsh environment. These conditions set high standards for the applied mechanical design, including the sealing quality of joints and assemblies, manufacturing processes, tolerances and materials.
The above often results in complicated constructions having e.g. vulnerable internal hydraulic piping posing many potential leaks. Therefore, a need exists for downhole tools that are relatively easy and safe to assemble and subsequently take apart during e.g. maintenance or overhaul.